The present invention relates to multiple beam separation control and, more particularly, to a refractive optical element, which controls separation of two closely spaced laser beams.
High speed or color printing requires a multiple beam light source. One possible multiple beam light source is a laser diode array which is currently expensive and difficult to fabricate. Another approach to providing a multiple beam light source is to integrate individual laser diodes to form the multiple light beam source.
The major problem with integrating individual laser diodes into a multiple beam light source is the large spacing between the individual laser diodes. The spacing or pitch between two adjacent individual laser diodes can be 100 microns or larger while the required spacing of the two adjacent light beams for printing uses is 25 microns or less, a difference of a factor of four or greater.
Beam separation control uses optical elements to contract the pitch or spacing between light beams.
Current technology can use single crystals, particularly calcite crystals, as beam separation control. However, these crystals cannot be artificially grown, which limits their availability and ability to be mass reproduced. The crystals require extensive fabrication and precision assembly.
Alternate methods of glass plates and miniature prisms are expensive and difficult to manufacture. Mechanical adjustment is required to set the center to center spacing of the adjacent beams.
Beam combiners, as their name indicates, are optical elements that combine two or more light beams into a single overlapping composite beam. Beam combiners can be refractive optical elements such as prisms, diffractive optical elements such as diffraction gratings and reflective optical elements such as dichroic or partially silvered mirrors. Beam combiners are distinctly different optical elements from beam separation control.
Beam splitter prisms can be used for beam separation control but this approach reduces the intensity of the output beam by half due to light loss caused by splitting the beam.
One possible beam separation control device is found in U.S. Pat. No. 5,566,024, commonly assigned as the present application and herein incorporated by reference. Two sets of two single blazed binary diffractive optical elements form a beam separation control apparatus for contracting two wider spaced parallel beams into two closely spaced parallel beams.
It is an object of the present invention to provide beam separation control by a single refractive optical element.